Trace metal monitoring in marine organisms and their living habitats permit to trace chronic or acute contaminations of marine ecosystems due to human activities. While dissolved trace metal ... [more ▼]

Trace metal monitoring in marine organisms and their living habitats permit to trace chronic or acute contaminations of marine ecosystems due to human activities. While dissolved trace metal concentrations give us an overall and punctual view over biota contamination status, bioindicator species put their bioavailable and possible toxic fraction in an obvious. However, difficulties mainly inherent to metal measurements in seawater lead field ecotoxicologists to study marine pollution essentially through the use of bioindicators alone. The technique of diffusive gradients in thin films (DGT) for the measurement of trace metals in aqueous solutions was introduced in the mid-ninetieth by Davison and Zhang. This passive probe accumulates labile trace metal species in proportion to their bulk environmental concentrations by maintaining a negative gradient between the environment and an ion-exchange resin (Chelex). DGTs average natural water trace metal concentrations over the deployment period, concentrate them and avoid matrix interferences, notably due to dissolved salts in seawater. Their deployment in passive and experimental monitoring studies permits to reliably measure labile trace metal concentrations and, jointly analysed with bioindicators, to estimate their bioavailability to marine organisms. This combined approach DGT-bioindicator was investigated in Calvi Bay (Corsica) through three monitoring studies. (1) DGTs were deployed in Posidonia oceanica bed, a Mediterranean seagrass forming dense meadows from the surface down to 40 meters depth, to study seasonal, spatial and bathymetrical variations of labile trace metal concentrations within this meadow. These concentrations were analysed jointly with Posidonia trace metal contents in order to quantify their bioaccumulation towards this primary producer, taking into account the seagrass biological cycle. (2) Portions of Posidonia meadow were also in situ experimentally contaminated with a mix of dissolved metals to study seagrass kinetics of pollutant accumulation and decontamination. Thanks to DGTs deployed inside contaminated mesocosms throughout experiments, Posidonia responses to known metal concentrations could be precisely quantified. (3) The blue mussel Mytilus galloprovincialis is widely used in trace metal monitoring programs. Mussels, stored in conchylicultural pouches, were transplanted for 3 months in contrasted stations of Calvi Bay (e.g. aquaculture farm, sewer, etc.) in parallel with DGTs. Such as for Posidonia, the complementary utilization of DGTs and mussels permitted to describe water contamination levels at the scale of the Bay, and their bioaccumulation towards mussels. These 3 studies demonstrate the usefulness of DGTs to monitor labile trace metals in an ecological and ecosystemic approach, in parallel with marine organisms, both indicators furnishing different and complementary informations about ecosystem functioning. [less ▲]

The harbor seal (Phoca vitulina) and the harbor porpoise (Phocoena phocoena) from the North Sea have experienced major fluctuations these last decades due to habitat loss, prey fluctuation and pollution ... [more ▼]

The harbor seal (Phoca vitulina) and the harbor porpoise (Phocoena phocoena) from the North Sea have experienced major fluctuations these last decades due to habitat loss, prey fluctuation and pollution of the marine environment. Recently, development of monitoring programs and non-invasive sampling techniques, including seal catches in Germany allowed blood sampling together with measurements of blubber thickness, body mass, sex and body length. This approach is complementary to the study of stranded and by-caught individuals sampled during necropsies. Essential (Se, Zn, Cu, Fe) and non-essential elements (T-Hg, MeHg, Cd, Pb), perfluorinated organochemicals (PFCs) polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) were measured in blubber and in blood (for selected compounds) of stranded, by-caught and free-ranging individuals from Belgian and German coasts. In contrast to Cd and Pb, hepatic T-Hg can reach concentrations as high as 2.1 μg.g-1 dry weight but depended on several factors including position in the trophic chain (inferred from δ13C and δ15N values), age group and the body mass. This level has been shown to generate in vitro toxicity on harbor seal lymphocytes. Organic compound analysis (PFCs, PCBs, PBDEs) revealed widespread dispersion of contaminants in the marine environment with higher concentrations in seals compared to porpoises in agreement with the higher trophic position of the harbor seal. However, metabolization of these compounds differed between the two species, as revealed by the higher contribution of the persistent BDE-47 and lower chlorinated and non-persistent congeners (e.g. CB 52, CB95) in tissues of harbor porpoises. T-Hg, PFCs, PCBs and PBDEs were detected in calves confirming maternal transfer to offspring. These pollutants are strongly suspected to affect the immune and endocrine systems as well as vitamin A metabolism and this raises concern about exposure-related health effects, especially in younger individuals. [less ▲]

Posidonia oceanica is a seagrass endemic to the Mediterranean Sea, and is able to form large monospecific areas, called meadows. These meadows shelter high biomasses and biodiversities of amphipod ... [more ▼]

Posidonia oceanica is a seagrass endemic to the Mediterranean Sea, and is able to form large monospecific areas, called meadows. These meadows shelter high biomasses and biodiversities of amphipod crustaceans. Moreover, It is now established that several species of these amphipods feed on the macro-epiphytes present on the leaves of the seagrass. Here, we performed in situ experiments to assess whether this grazing activity could impact the dynamics of the leaves’ epiphytic cover, and thus influence the functioning of the meadow as an ecosystem. We used microcosms containing monospecific populations of 3 amphipods taxa (Apherusa chiereghinii, Dexamine spiniventris and Gammarus spp.), and placed them directly in the meadow, at a depth of 10m. Biomasses of erected macroalgae and erected animals (hydrozoans, bryozoans) were lower in all grazed treatments. However, none of the studied taxa seemed to consume encrusting epiphytes, either vegetal or animal. This selective grazing pressure by amphipods may release encrusting epiphytes from competition for space, light and/or nutriments with the fast-growing erected algae, and could thus play an important role in the structuring of the epiphytic cover from P. oceanica leaves. Moreover, this top-down control might keep erected algae biomass to a normal, sustainable level, therefore also benefiting the seagrass itself. Our results also indicate that amphipod trophic activity caused nitrogen enrichment in both grazed (erected algae) and non-grazed (encrusting algae & seagrass leaves) vegetal tissues. A plausible interpretation could be that sloppy feeding and excretion by the grazers enhanced availability of this nutrient, which is typically limiting for photosynthesis in shallow P. oceanica meadows. This emphasizes the fact that grazing is not a simple negative interaction, but that it can also benefit the primary producers. Our results thus indicate that amphipods from P. oceanica meadows seem to be bound to the epiphytic cover of the leaves by complex and multilateral trophic interactions, and have an indirect influence on the seagrass itself. Amphipods may therefore play an important part in the functioning of the epiphyte/seagrass/grazer system of these meadows, and thus act as ecosystems engineers. This abstract is dedicated to the freshly born Adèle and Côme. [less ▲]

Increasing human pressure along Mediterranean coastlines raises the need to define sensitive bioindicators that provide an early response to nutrient enrichment. We performed multiscale carbon and ... [more ▼]

Increasing human pressure along Mediterranean coastlines raises the need to define sensitive bioindicators that provide an early response to nutrient enrichment. We performed multiscale carbon and nitrogen stable isotope analyses on the limpet Patella caerulea, the snail Monodonta turbinata, epilithic biofilms, and the macroalga Rissoella verruculosa inhabiting the rocky midlittoral zone. Samples were seasonally collected in 2006 from 5 sites exposed to a range of anthropogenic discharges in the Revellata Bay area and in Marseille harbour (France). All bioindicators exhibited strongly elevated δ15N values at impacted sites compared to pristine ones, which revealed the biological availability of anthropogenically derived nutrients. Only epilithic biofilms tended to show both the occurrence of nutrient pulses during the tourist season and a δ13C response at impacted sites. In contrast to macroalgae, which exhibited a somewhat equivocal signal, gastropods and especially M. turbinata provided the best time-integrated picture of the graduated exposure of the 5 sites to anthropogenic impact. Results also showed first evidence of large isotopic variability at a scale of tens of metres, close to that found at the kilometre scale. The intra- and interspecific isotopic variability in gastropods may be explained by the patchiness of resources and specific morphological and behavioural features, but these factors do not greatly hamper their potential as early bioindicators of wastewater disturbances. [less ▲]

Risso’s dolphins, pilot whales and sperm whales rarely strand in the northwestern Mediterranean. Thus, their feeding ecology, through the analysis of stomach contents, is poorly known. The aim of this ... [more ▼]

Risso’s dolphins, pilot whales and sperm whales rarely strand in the northwestern Mediterranean. Thus, their feeding ecology, through the analysis of stomach contents, is poorly known. The aim of this study was to gain further insight into the segregation/superposition of the diet and habitat of Risso’s dolphins, pilot whales and sperm whales using chemical tracers, namely, stable isotopes (d13C, d15N) and orga- nochlorines. Significantly different d15N values were obtained in Risso’s dolphins (11.7 ± 0.7‰), sperm whales (10.8 ± 0.3‰) and pilot whales (9.8 ± 0.3‰), revealing different trophic levels. These differences are presumably due to various proportions of Histioteuthidae cephalopods in each toothed whale’s diet. Similar d13C contents between species indicated long-term habitat superposition or corroborated impor- tant seasonal migrations. Lower congener 180 concentrations (8.20 vs. 21.73 lg.g􏰀1 lw) and higher tDDT/ tPCB ratios (0.93 vs. 0.42) were observed in sperm whales compared with Risso’s dolphins and may indi- cate wider migrations for the former. Therefore, competition between these species seems to depend on different trophic levels and migration patterns. [less ▲]

Numerous freshwater species are consumed or exploited through artisanal fisheries in the rivers of the islands of Guadeloupe, French West Indies. Autochthonous production of organic matter is limited in ... [more ▼]

Numerous freshwater species are consumed or exploited through artisanal fisheries in the rivers of the islands of Guadeloupe, French West Indies. Autochthonous production of organic matter is limited in these flowing rivers and is mainly represented by scarce filamentous green algae and an abundant epilithic biofilm growing on wet stones in the river bed. Stable isotope analysis was used to quantify the relative importance of biofilm and other riverine allochthonous and autochthonous food sources in the diet of tropical shrimps (Palaemonidae, Atyidae and Xiphocarididae) and fishes (Gobiidae and Eleotridae) consumed by the local people. The epilithic biofilm was exploited by most species, constituted an important source of autochthonous carbon and wasan important source of organic matter production at the base of freshwater food webs in Caribbean rivers. Biofilm percentages in the diet reached 32% for molluscs, 85% for atyid shrimps, 29% for xiphocaridid shrimps, 14% for palaemonid shrimps and 13% for fish. Assessment of biofilm in nine rivers showed that blue and red cyanobacteria were quantitatively dominant with a moderately rich diatom flora. These results address the interactions between river biofilm and Caribbean freshwater fauna where trophic links between consumers and their potential resources have poorly been documented. [less ▲]

Concentrations of organochlorine pesticides and stable isotope ratios of nitrogen and carbon were measured in a tropical freshwater ecosystem to evaluate the contamination level of biota and examine the ... [more ▼]

Concentrations of organochlorine pesticides and stable isotope ratios of nitrogen and carbon were measured in a tropical freshwater ecosystem to evaluate the contamination level of biota and examine the bioaccumulation patterns of pollutants through the food web. Chemical analyses showed a general and heavy contamination of the entire food web. They revealed the strong accumulation of pollutants by juveniles of diadromous fishes and shrimps, as they re-enter the river. The role of ecological factors in the bioaccumulation of pesticides was evaluated. Whereas the most persistent pollutants (chlordecone and monohydro-chlordecone) were related to the organisms diet and habitat, bioaccumulation of b-HCH was only influenced by animal lipid content. The biomagnification potential of chlordecone through the food chain has been demonstrated. It highlighted the importance of trophic transfer in this compound bioaccumulation process. In contrast, bioconcentration by passive diffusion from water seemed to be the main exposure route of biota to b-HCH. [less ▲]

Downward flux of zooplankton faecal pellets and carcasses was studied during and after the spring bloom in an oligotrophic coastal area of the Western Mediterranean using a « swimmer-excluding » sediment ... [more ▼]

Downward flux of zooplankton faecal pellets and carcasses was studied during and after the spring bloom in an oligotrophic coastal area of the Western Mediterranean using a « swimmer-excluding » sediment trap. Zooplankton detritus retrieved in the trap were comprised of cylindrical faecal pellets (from meso- and macrozooplankton) and copepod carcasses with a respective carbon flux of 0.05 - 2.69 mg m-2 d-1 and 0.42 - 4.37 mg m-2 d-1. Carbon and nitrogen flux of carcasses always exceeded that of faecal pellets, except at the beginning of the bloom due to a higher contribution of macrozooplankton faecal material. During the peak of phytoplankton biomass, total faecal flux essentially comprised of copepod faecal pellets (68 - 86% of the total faecal carbon), whereas before and after this period, macrozooplankton faecal material dominated (88 - 91% of total faecal carbon flux). Copepod faecal flux was positively correlated with phytoplankton biomass. Estimates of non-predatory biomass mortality rates (from < 0.01 to 0.05 d-1) were negatively correlated with chl a with a time lag of 12 days and were lower than predatory mortality values reported in the same area. The paper discusses the relative importance of carcasses versus faecal pellet flux and of non-predatory versus predatory mortality, as well as the potential role of these zooplankton detritus in supporting the production of benthos in oligotrophic areas. [less ▲]

2. Nitrogen stable isotopes (hereafter delta 15N) were used to place termites from French Guiana rainforests along a wood-soil decomposition gradient, to test (i) whether feeding group assignation based ... [more ▼]

2. Nitrogen stable isotopes (hereafter delta 15N) were used to place termites from French Guiana rainforests along a wood-soil decomposition gradient, to test (i) whether feeding group assignation based on morphological characters was accurate and actually represented diet specialisation thresholds, and (ii) to what extent the dietary specialization of species is explained by phylogeny (phylogenetic autocorrelation). 3. delta 15N values vary over a range of 13 parts per thousand, suggesting that diet diversification contributes to the high species diversity in French Guiana. delta 15N values span a similar interval in all Termitidae subfamilies. Ranges of different subfamilies broadly overlap, although each of them diversified preferentially on one side of the wood-soil decomposition gradient. Congeneric species share similar feeding habits, whereas distant species tend to feed on distinct substrates. 4. Feeding groups did not completely match stable isotope data: there was no discontinuity between Groups III and IV, and no correlation between anatomical criteria used to distinguish these groups and delta 15N values. Nor was there any consistent difference in delta 15N values between wood feeders of the families Rhinotermitidae (Group I) and Termitidae (Group II). We also suggest that species feeding outside the wood-soil gradient should be distinguished for their peculiar feeding requirements. [less ▲]

In the Mediterranean Sea, the seagrass Posidonia oceanica is affected by many threats from anthropogenic sources. One of them is the increasing development of fish farming, which is responsible of the ... [more ▼]

In the Mediterranean Sea, the seagrass Posidonia oceanica is affected by many threats from anthropogenic sources. One of them is the increasing development of fish farming, which is responsible of the destruction of some meadows. Within troubles cause by those fish farms on the surrounding environment, the increase of phytoplankton biomass in the water column (leading to a shading effect) and a modification of the sediment are often cited as a reason of seagrass disappearance. To understand how those troubles are affecting P. oceanica and its sedimentary compartment, in situ experiments were led during three months, from the end of May til the end of August 2009, in STARESO (STAtion de REcherches Sous-marines et Océanographiques, Corsica, France), at a depth of 10 meters. The shading was mimicked by three replicated shading frames (3 x 1 m), which stopped around 50 % of the incident light. To modify the sedimentary compartment, some sediment was taken from under the fish farm of Calvi (Corsica, France) and added once a week on marked zones in the seagrass meadow. Those sites were compared with a control site, situated in the same meadow. Samples were taken once a month and consisted in pore water, sediment cores and shoots of P. oceanica. An estimation of the density of the meadow in every sampling zones was also performed. Measured parameters are the concentration of nutrients in pore water, grain size, redox potential discontinuity (RPD), biomass of bacteria, organic matter, meiofauna and microphytobenthos within the sediment, total carbon and nitrogen in the sediment and leaves, the length, width and biomass of leaves and shoots, the biomass of epiphytes and the content of chlorophyll a in leaves. During those experiments, Posidonia oceanica was not very affected. However, some parameters of the sedimentary compartment were modified (RPD, biomass of bacteria, organic matter, nutrients in pore water,…), suggesting a modification in the functioning of the ecosystem. These results are important because they show that the sedimentary compartment reacts more rapidly to threats then the seagrass itself. So, it could be an interesting tool in quality assessments. [less ▲]

Meiofaunal communities of the endemic Mediterranean seagrass, Posidonia oceanica, were sampled in five different habitats characterised by different degradation level of macrophytodetritus. In term of ... [more ▼]

Meiofaunal communities of the endemic Mediterranean seagrass, Posidonia oceanica, were sampled in five different habitats characterised by different degradation level of macrophytodetritus. In term of abundance, harpacticoid copepods represent half of the community followed by nematodes and polychaetes. Two meiofauna communities were distinguished: (1) a benthic community of meiofauna, living in the sediment or on highly fragmented macrophytodetritus, and (2) a foliar, epiphytal community associated with seagrass leaves and low fragmented macrophytodetritus leaves. They differed significantly in their harpacticoid copepod family composition. The benthic community consisted mainly of families like Tisbidae and Miraciidae, while the epiphytal community was dominated by families like Thalestridae and Laophontidae. These differences in composition may also imply a differential functional diversity. Trophic biomarkers (stable isotopes, fatty acids) were used to identify the major sources of organic matter contributing to the copepods diet and hence to gain insight in the overall carbon flux. Harpacticoid copepods showed preferences to feed upon the epiphytal biofilm community composed of bacteria, diatoms, fungi and microalgae. Copepods used the seagrass and detritus material merely as substrate, but were attracted to the biofilm rather than the plant material which is rich in structural carbohydrates difficult to assimilate by animals (i.e. lignin, cellulose, ...). Since harpacticoid copepods showed to use different sources of carbon, unravelling the contribution of each of them and the role of the degradation level of the detritus for food selectivity is the next step forward. [less ▲]